In a survey given in 1985, people were asked to list their friends in response to the question “Over the last six months, who are the people with whom you discussed matters important to you?” The most common number of friends listed was three; 59 percent of respondents listed three or more friends fitting this description. The same survey was given again in 2004. This time the most common number of friends was zero. And only 37 percent of respondents listed three or more friends. Back in 1985, only 10 percent indicated that they had zero confidants. In 2004, this number skyrocketed to 25 percent. One out of every four of us is walking around with no one to share our lives with.

This is sad, and for more reasons than you might expect. We need friends to keep us healthy. Lack of social support predicts all causes of death.

Having few friends is more dangerous than obesity and is the equivalent health risk of smoking 15 cigarettes a day.

Julianne Holt-Lunstad, Ph.D., professor of psychology at Brigham Young University, did a meta-analysis of 148 studies and concluded that a lack of social support predicts all causes of death. People with a solid group of friends are 50 percent more likely to survive at any given time than those without one. Holt-Lunstad calculated that having few social ties is an equivalent mortality risk to smoking fifteen cigarettes a day and even riskier than being obese or not exercising!

You need friends for self-knowledge — because your friends often know more about you than you do.

They can truly know us, sometimes better than we know ourselves. Specifically, friends are better at describing our behavioral traits than we are, says Simine Vazire, Ph.D., a psychologist who runs the Personality and Self-Knowledge Lab at Washington University in St. Louis. “Friends can assess whether we are funny, dominant, or charming better than we can,” she says. They may not be better than we are at knowing what we are feeling and thinking, unsurprisingly, but they are superior at guessing our IQs. (Incidentally, it’s often the case that we judge ourselves as less intelligent than we are.)

And friends make you happier than pretty much anything else in life.

Got three friends at work? You’re 96% more likely to be extremely satisfied with your life.

If you can count at least three dear friends at the office, you are 96 percent more likely to be extremely satisfied with life in general…

Fowler and Christakis found that you are about 15 percent more likely to be happy if one of your friends is happy (overall, not in any particular moment). Even if a friend of your friend is happy, you’re 10 percent more likely to be in a contented state. “We found that each happy friend a person has increases that person’s probability of being happy by about 9 percent. Each unhappy friend decreases it by 7 percent,” they write. Since these stats imply that happiness is more contagious than unhappiness, they conclude that “the more, the merrier” holds true, despite what is usually said about quality over quantity in friendships. They also found that an additional friend amounts to two fewer days of feeling lonely each year. “Since on average (in our data) people feel lonely forty-eight days per year, having a couple of extra friends makes you about 10 percent less lonely than other people. Interestingly, the number of family members has no effect at all.”

Having a friend you see on most days is the happiness equivalent of an extra 100K a year.

Nobel Prize winner Daniel Kahneman, Ph.D., of Princeton, and colleagues conducted an innovative study about a decade ago that captured people’s happiness “in the moment” as they went about their daily lives. They found, controversially, that time with friends is even more enjoyable than moments with spouses or children.

Not that there’s anything wrong with spouses and kids but time with friends does not involve the same responsibilities — and we all need a break.

Beyond that, time with friends as a couple has been shown to improve long term relationships.

Most intriguing was how couples rated their own relationships more positively after interacting with other pairs. Married partners fall into routine interactions and often fail to make the effort to entertain and please as they did when they were winning each other over. Putting your best self forward for new friends allows you to shine and to see your partner through new eyes as she shines, too. Maintaining older mutual friendships also strengthens the bond between long-term partners: Having people around who think of the two of you as a unit, who admire your relationship, and who expect you to stay together can sustain you through times of doubt or distance.

And You Will Lose Friends

Within seven years, half of your close friends will not be around anymore.

A study by a Dutch sociologist who tracked about a thousand people of all ages found that on average, we lose half of our close network members every seven years. To think that half of the people currently on your “most dialed” list will fade out of your life in less than a decade is frightening indeed.

So if you want to keep close friends in your life, it’ll take some effort. But what do you need to do?

Here’s what some of the latest research has to say.

What To Do

Daniel Hruschka reviewed studies on the causes of conflict in friendship and found that the most common friendship fights boil down to time commitments. Spending time with someone is a sure indicator that you value him; no one likes to feel undervalued.

This is also the part of friendship that makes us happiest — doing things together.

It’s no news flash that friends make us happy, but Meliksah Demir, Ph.D., a professor at Northern Arizona University, has drilled down to reveal exactly what about friendship warms our hearts. It turns out that companionship— simply doing things together— is the component of friendship that most makes us happy. And the reason friends make us happy, Demir has concluded, is that they make us feel that we matter.

Mere proximity — being nearby, is one of the most powerful drivers of friendship — far more than personality. So be around.

Yet research does not show that friends are particularly alike in personality, granting scientific credibility to hundreds of romantic comedies wherein the uptight leading lady has a free spirit for a sidekick and the charismatic main man has a buffoonish buddy…Half a century ago, researchers came up with the “proximity theory” of friendship— that we befriend people who live geographically close to us or who frequently cross our path because they go to our school, grocery store, office, or favorite diner. Proximity, first and foremost, grants easy opportunities to meet. But also, familiarity breeds positivity. Called the “mere-exposure effect,” it’s a phenomenon that is widely documented: Just seeing someone over and over can make you like him or her more.

‘If you’re not willing to be bored sometimes, you can’t have friends,’ ” Jacob says. “Sometimes friends are going to drone on about their mother or something that you don’t quite care about. But it’s not just about what they can do for you, it’s a deeper thing. You can’t expect to always be entertained, or to always feel like everything is one hundred percent reciprocal.” Jacob, who likes to entertain, says, “I’m willing to invite someone to dinner ten times and never see their house, because if you get into the cycle of pettiness, you won’t end up having any friends.”

Be flexible. Having social skills means adapting to your environment, not stubbornly “being who you are.”

Children who are natural social stars, Rubin adds, present themselves “successfully to others by putting on somewhat different faces for different audiences.… They understand when to put on which face, without ever appearing shallow or false to others and without feeling like fakes or frauds. In short, these are children who are sensitive and responsive to social cues.” This is the child who knows how to work the room with jokes or dance moves at her own birthday party with her adoring relatives, but who also knows to hang back and let a friend shine at his birthday party.

And this one is key: Support the person’s view of themselves and make them feel good about their pursuits.

Best friends don’t have to share an identity per se, but they do need to support the other’s view of himself and make each other feel great about their pursuits. Weisz asked a group of college freshmen about their close friends and used questionnaires to determine whether they received social identity support from them. She then followed up five years later, when the students had graduated and moved off campus. Social identity support didn’t predict whether the friendships generally endured, but it did predict whether one of the friends became a best friend. Part of maintaining a close friendship, Weisz points out, is supporting someone’s identity as it inevitably shifts over time.